Sorting an array

I was following this tutorial that shows you how to sort an array. My action looked like this:

def index
@articles = NodeType.find(1).nodes + NodeType.find(2).nodes
@articles.sort_by { |article| article.updated_at }
end

But that didn't work! It wasn't sorting at all.. at least as far as I could tell. Strange, because this worked:

def index
@articles = NodeType.find(1).nodes + NodeType.find(2).nodes
@articles = @articles.sort_by { |article| article.updated_at }
end

It seems you have to assign it to an object first, before returning it.